1. Field of the Invention
The present invention relates to a technique of controlling a motor using a resolver output.
2. Description of the Background Art
A technique of calculating a motor rotation speed using a resolver and controlling the motor based on the calculated rotation speed is known. Generally, a resolver output contains an error. To eliminate an influence of this error, various techniques of correcting for a detected angle of the resolver have conventionally been proposed.
For example, Japanese Patent Laying-Open No. 2004-222448 discloses a technique of measuring time periods T1 to T12 until the detected angle of a resolver becomes 60°, 120°, . . . and 720°, respectively, calculating a shift angle Δθn every 60° using measured time periods T1 to T12, and substituting calculated shift angle Δθn into the expression θn=n×60°+Δθn (n=1 to 11), thereby performing angle correction every 60°. It is described that this technique can drive a motor while preventing a control failure even if the detected angle of the resolver contains an error.
It is known that a resolver output contains an error synchronized with rotation of a rotor. A technique for eliminating this error includes a technique of calculating the rotation speed of the motor based on the result of measuring a time period in which a resolver output completes one cycle (resolver cycle).
There is another technique of dividing 360° corresponding to one cycle of a resolver output into a plurality of sections, and measuring the resolver cycle every time the detected angle of the resolver exceeds each division border, thereby calculating the rotation speed. With this technique, the calculation cycle of the rotation speed can be made shorter than the resolver cycle, so that the rotation speed can be calculated with accuracy even at low motor rotation speeds. However, in the case where determination about division border exceeding is implemented via software, the division border exceeding cannot be measured correctly in such a long calculation cycle of performing at least one calculation per division border, resulting in degraded calculation accuracy of the rotation speed.